In this well-documented book,
Ehrlich discusses a number of controversial issues: why people
evolved an upright posture; what happened to the Neanderthals; how
our brains work; how language evolved; what led to the very sudden
appearance of modern human beings; why race is an outdated concept;
how can we account for altruism and aggression; why humans enjoy
sex all year round; why women have orgasms; why many of us crave
hot fudge sundaes; how religion and states evolved; and the origin
of ethics.

Ehrlich, author of The Population
Bomb and many other books and scientific articles, is Bing
Professor of Population Studies and president of the Center for
Conservation Biology at Stanford.

In Human Natures, he
expresses concern about the growing resurgence of genetic
determinism -- the belief that human DNA contains "instructions"
that dictate behavior, including so-called "genes for rape," "gay
genes," "criminal genes" and "genes for intelligence."

"There is an unhappy predilection,
especially in the United States, not only to overrate the effect of
genetic evolution but also to underrate the effect of cultural
evolution," writes Ehrlich.

"Uniquely in our species, changes in
culture have been fully as important in producing our natures as
have changes in the hereditary information passed on by our
ancestors," he adds.

Take, for example, the popular
belief that human males are genetically wired to be more
promiscuous than females.

"Women, like men, evolved to be
smart," says Ehrlich, "and they certainly don't need to be rocket
scientists to understand that they make a bigger potential
commitment to each sex act than do men. That alone, rather than an
evolved tendency in men to reproduce more, could explain
differences in attitudes toward fidelity."

And on the question of whether human
beings are innately aggressive, Ehrlich points out that we are "at
least as often peaceful and resolve conflicts nonviolently. Maybe
we should talk about us as being the 'conciliatory
apes.'"

He dismisses the notion of the
"selfish gene" --- the idea that genes are simply tiny,
self-reproducing units with goals of their own.

"Much of the problem," according to
Ehrlich, "traces to the field of evolutionary psychology, where
knowledge of genetics and evolution tends to trail far behind the
knowledge of psychology. Indeed, talk about genes being
'self-replicating' or 'selfish' is very misleading. Genes cannot be
reproduced except by being imbedded in a complex cellular mechanism
-- they're about as self-replicating as a printed page lying in a
copying machine.

"Furthermore," he maintains, "it is
critical that genes act in concert and not interfere with the
functioning of other genes. Thus if one is silly enough to assign
human-like motivation to them, it would be as sensible to describe
them as 'cooperative' as to call them 'selfish.'

"The influences of an animal's genes
depend upon the environment in which it lives, and there can be no
environments without genes, since for the physical world to be an
'environment' there must be organisms, and all organisms modify
their environments," he adds.

"Genes and environments are
fundamentally connected," notes Ehrlich, "and they interact in
complex ways -- something we must always keep in mind when we
necessarily, but artificially, separate them for purposes of
analysis and discussion."

Ehrlich contends that the
long-standing debate over "nature vs. nurture" is largely a false
dichotomy.

"Especially unfortunate," he says,
"is the common view of the public that if something is 'genetic' it
can't be altered. Even the behavioral effects of Down syndrome,
traceable to a major genetic defect -- the presence of an extra
chromosome -- can be greatly influenced by providing an affected
child with a stimulating environment."

Human Natures emphasizes
that, while genetic evolution clearly has influenced human
behavior, a much more important factor is cultural evolution --
"changes in the vast body of non-genetic evolution that humanity
stores in its brains, books, buildings, computers, films and the
like."

From a biological perspective,
Ehrlich points out, the human genome does not have remotely enough
genes to program the connections in our brain that control
behavior.

"There are on the order of one
billion connections for every gene," he argues. "Our 'gene
shortage' is one reason human infants and young children are so
helpless. Their helplessness allows the physical and cultural
environments to do the brain programming that our hereditary
endowment couldn't manage. It's that environmental input that gives
us the adaptability that is the hallmark of humanity. We could
never have evolved as genetically controlled robots."

Ehrlich, known for his advocacy of
conservation, concludes Human Natures with a discussion on
the evolution of environmental ethics and other human
values.

"A modern knowledge of biological
and cultural evolution helps us grasp what kinds of animals we are,
where we came from and how we fit into the natural world," he
writes.

Ehrlich is convinced that many
scientists know already the directions in which solutions to the
population-environment crisis lie.

"Gradual and humane reduction of the
size of the human population, limiting of wasteful per capita
consumption among the rich to allow room for increased consumption
by the poor, use of more environmentally benign technologies and
increased equity among and within nations will all be
required.

"That's what we need to do,
and interdisciplinary teams of scientists are even starting to
figure out how we might do it. For instance, it's clear that
individual economic incentives must be brought into alignment with
society's long-term best interests."

But pursuing the "how" goal will
require much more effort, Ehrlich claims.

"Our cultural evolution on the
technological front, our ability to do, has vastly outpaced
cultural evolution in knowledge of the environment and human
relations, our ability to understand," he concludes. "To
change our ways we must know ourselves, including our history. I
hope Human Natures will be a contribution to building that
understanding."

Ehrlich joined the department of
biological sciences at Stanford in 1959. In the early 1960s he
developed the theory of coevolution with then Stanford faculty
member Peter Raven. Their work began one of the most active and
important areas of evolutionary-ecological theory.

Ehrlich is a member of the National
Academy of Sciences and a fellow of the American Association for
the Advancement of Science, the American Academy of Arts and
Sciences and the American Philosophical Society.

He also is recipient of the Sierra
Club's John Muir Award, the World Wildlife Fund's Gold Medal Award,
a MacArthur Prize Fellowship, the Crafoord Prize of the Royal
Swedish Academy of Sciences (given in lieu of a Nobel Prize in
areas where the Nobel is not given) and the United Nations'
Sasakawa Environment Prize. SR